The present invention relates to apparatus and methods of inspecting the orifice plates used in fluid jet devices for purposes of determining orifice dimensional characteristics. More particularly, the present invention relates to an optoelectronic system for determining the relative sizes of the orifices, the distribution of the orifice sizes along the length of the orifice plate, and flaws in individual orifices.
In fluid jet printing, an orifice plate is disposed below a distribution bar having a plenum whereby fluid flows from the plenum through the orifices of the orifice plate for deposition on a substrate. Generally, filaments formed as the fluid emerges from the orifices are selectively charged by a charge electrode. The droplets formed by the filaments flow through an electrostatic field provided by a deflection electrode. The charged droplets are displaced from a straight downward path by the electrostatic field onto a catched structure, whereas the uncharged droplets flow straight downwardly for deposition on the substrate, e.g., a textile fabric.
With the evolution of fluid jet printing and applicators, the size of the orifices has become a critical factor for achieving precise control over the patterns provided on a substrate, for example, a textile fabric about 1.8 meters in width. In pattern-generating fluid jet printing devices for textile fabrics, a 72" orifice plate may have 72 or 144 orifices per inch for a total of 5,063 or 10,126 holes over its length, respectively. The orifices are nominally in the 1-4 mil size range. The specific orifice size is dependent on the end use of the orifice plate, and for optimum flow characteristics, the variation in the orifice area should not exceed about .+-.1178 %.
For high resolution, for example when creating patterns in fabrics, it is essential that the orifice size, i.e., orifice area, be uniform throughout the length of the plate within the above-mentioned tolerance range. Inspection of orifice plates and particularly the size of the orifices to determine whether the orifices lie within this tolerance range, is a tediuous, time-consuming and error-prone process when done conventionally by inspection of the orifices through a microscope. More importantly, size errors are of such small magnitude as to be below the diffraction limit of light microscopes. Microscopes, moreover, do not enable the determination of whether the orifices are out-of-round, or otherwise irregularly shaped.
The present invention provides apparatus and methods for automatically inspecting the orifices of the orifice plate to determine the relative areas of the orifices, the distribution of the orifice sizes along the length of the orifice plate and to detect flaws in individual orifices. To accomplish this, the present invention provides a support frame on which the orifice plate is mounted. A carriage is mounted on the support frame for movement longitudinally therealong on suitable guide rails. In a preferred form, an endless belt and pulley arrangement is provided to move the carriage back and forth along the support frame and hence to traverse the length of the orifice plate. The carriage carries as part of an optoelectronic inspection system, a laser light source on one side of the orifice plate and an optical detector on the opposite side of the orifice plate whereby the laser light beam passes through the orifices for detection by the detector one after the other as the carriage traverses the length of the orifice plate. The intensity of the detected light is proportional to the area of the individual orifice through which the laser light has been transmitted. Thus, the detector generates light intensity signals which are proportional to the area of the orifices and which signals are processed, digitized, and further processed by a data processor to determine orifice size distribution along the plate and flaws of the individual orifices. While the present invention is herein described using a laser as the energy transmitting source and an optical detector as the energy receiving detector, it will be appreciated that the energy source and detector could be other types of energy transmitting sources and receivers, respectively, for example of the electromagnetic radiation type.
In accordance with the present invention, there is provided apparatus for determining a dimensional characteristic of orifices in an orifice plate useful for fluid jet printing comprising means for mounting an elongated orifice plate, optical light emitting and detection means including a light source on one side of the orifice plate for directing light through the orifices thereof and a light detector on the opposite side of the orifice plate from the light source for receiving light directed through the orifices by the light source. Means are additionally provided for effecting relative movement of the optical means and the mounting means for directing light through the orifices for detection by the detector. The light detector is operable to generate signals proportional to the intensity of the received light, and means for processing the signals to determine the dimensional characteristic of the orifices are provided.
In another aspect of the invention, there is provided apparatus for automatically determining the uniformity of the apertures in a member having an array of apertures comprising holding means for disposing an energy source adjacent the array of apertures, means for moving the apertures relative to the energy source, means for sensing the amount of energy passing through the apertures and for generating electrical signals indicative thereof, and processing means responsive to the electrical signals for generating signals indicative of the degree of uniformity of the apertures in the array.
In a further aspect of the present invention, there is provided a method for determining a dimensional characteristic of an orifice in an orifice plate useful for fluid jet printing including the steps of disposing a light source on one side of the orifice plate for directing light through an orifice thereof, disposing a light detector on the opposite side of the orifice plate for detecting light passing through the orifice from the light source, generating an electrical signal proportional to the intensity of the detected light and processing the electrical signal to determine the dimensional characteristic of the orifice.
A still further aspect of the present invention provides a method for automatically determining in a measurement system the uniformity of the apertures in a member having an array of apertures comprising the steps of disposing an energy source adjacent the array of apertures, moving the apertures relative to said energy source, sensing the amount of energy passing through the aperture and generating electrical signals indicative thereof, and processing the electrical signals to generate signals indicative of the degree of uniformity of the apertures in the array.
Accordingly, it is a primary object of the present invention to provide novel and improved apparatus and methods for inspecting an orifice plate useful in jet printing devices for purposes of determining the relative sizes of the individual orifices, the distribution of the orifice sizes along the length of the orifice plate and flaws in individual orifices.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.